The present invention relates to a method and apparatus for mounting sheet material in a frame and, more particularly, to a method and apparatus for stress-free mounting of frangible sheet material such as glass in a metal frame.
There are numerous applications in which frangible sheet material is mounted in and supported by a circumscribing metal frame. For example, sheet material such as glass is commonly mounted in a metal frame for application in sliding glass doors, shower enclosures and doors, doors for industrial equipment and windshields on such items as boats. The present invention is particularly useful in the mounting of curved glass into metal frames wherein the metal frame may be subject to deflection stresses. For example, the invention is particularly useful in minimizing stress transmitted to curved glass sheets used in the windshields on a boat deck in which the deck may be subject to transverse deflection thereby stressing the glass held within a metal frame surrounding the glass. The glass sheet and metal frame forms a windshield for the boat and is typically fastened to the deck of the boat such that the lower metal frame of the windshield is fixed to the boat and flexes with any motion of the deck. In any of the above-described applications, the metal frame or track protects the edge of the glass sheet and provides for a method of mounting or attaching the glass sheet to some other structure.
While the present invention is useful in the mounting of any form of frangible sheet member into a metal frame, the invention will be described herein with regard to one particular application of mounting of a frangible sheet member into a metal track for use on a boat. In this application, the combination of the metal frame or track with the frangible sheet member creates a windshield for the boat. By way of example, many of the windshields used on boats are generally triangular shaped, starting at a height of about 1xc2xd to 2 feet at a forward center line of the boat and terminating at essentially a point along a side of the boat. In this triangular windshield configuration, the windshield comprises a triangular shaped, curved glass sheet mounted into upper and lower metal tracks. The upper and lower tracks are normally fastened to one another at a side of the boat. A separate short track section connects the upper and lower track sections near the forward center line of the boat to complete the surrounding metal frame for the windshield. Typically, the metal frame is formed from aluminum and includes a track into which the edge of the glass sheet fits. In a conventional windshield, the aluminum track includes a rectangular channel in which an elastomeric gasket is fitted. The gasket may be formed of vinyl or other suitable elastomeric material. The gasket is shaped to have the same configuration as the track into which it fits and defines a separate channel for receiving an edge of the glass sheet. In general, the gasket is designed to have a very tight fit about an edge of the sheet when the glass sheet and gasket are forced into the channel in the metal track. In one prior art system, the glass track and gasket are bonded together by using an adhesive material in the channel. Typically, holes are cut into the gasket material adjacent to the bottom of the channel and a bonding material inserted into these holes prior to forcing the glass sheet into the gasket and channel combination. Once the adhesive material has set, it will bond the glass sheet to the metal track. A typical type of adhesive material used for this purpose is a urethane bonding material.
One of the problems which has been identified with this type of assembly is that the edges of the gasket material adjacent to the cut out sections or holes are not firmly maintained within the channel in the track. While these side edges can be pushed down into the channel, it is not unusual for the line that is formed by the edge of the gasket material along the glass sheet to be noticeably deformed and detract from the overall appearance of the windshield. Further, the tight fit between the glass sheet and the metal track allows stresses imparted on the metal track to be directly transferred to the glass sheet. Any stresses that are transverse to the direction of the glass sheet tend to want to deform the glass sheet and can lead to cracking or breaking of the sheet.
In addition to the above-described issues regarding the transfer of stress to the glass sheet of the windshield assembly, in boat applications, movement of the deck translates into additional stress placed on the portion of the windshield frame that is attached to the deck. Accordingly, it would be desirable to provide an attachment mechanism for a windshield to a deck which reduces the amount of stress transferred from the deck to the windshield frame.
Still another issue which arises in the context of the use of metal frame members for supporting frangible sheet materials is the connection of attachments to the frame member to enable coupling of other devices to the frame. For example, it is common to attach metal buttons to the frame of a boat windshield in order to couple a canvas cover to the windshield. In this particular application, the frame member for the windshield includes a horizontal slot which can be used to receive a plastic insert into which a threaded portion of a button can be screwed. In that application, threading the portion of the button into the plastic insert expands the insert and clamps it tightly within the frame member. However, it is not uncommon for the plastic to deform or be worn and allow the button to become loose and slide or even be lost from the frame member. Accordingly, it would be desirable to provide a more secure mounting for such attachments to a frame member of a windshield.
The present invention addresses the problems associated with stress imparted to a glass sheet through a metal track and also the problem associated with appearance or cosmetics of an assembled glass sheet and metal track when a conventional elastomeric gasket is not firmly seated within a channel of the metal track to support the glass sheet. In one form, the present invention eliminates the use of the elastomeric gasket of the prior art type and replaces the gasket with an elastomeric support member that is positioned within the channel of the metal track to temporarily support the glass sheet. Permanent support of the glass sheet is then provided by utilizing a bonding agent to adhesively bond an edge of the glass to the metal track. Preferably, the bonding agent is a urethane bonding agent or other suitable bonding agent that has a durometer reading of less than about 85 to 90 after the bonding agent has set. The temporary elastomer support sections may be short sections of elastomeric material laid into the channel on the bottom of the track and having sufficient length and spacing to adequately support the glass sheet in the metal track until such time as the bonding agent has set. The bonding agent may simply comprise periodic globules of the agent between the temporary elastomeric supports. Since the channel-shaped gaskets typical of the prior art provided an elastomeric spacing between sides of the glass sheet and the metal track, the absence of these elastomeric gaskets leaves a narrow space adjacent to each side of the glass sheet inserted into a channel of the track. The present invention utilizes a plastic insert in the form of an elongated strip of material that can be snapped into place between the glass sheet and the upper edges of the channel to fill the space between the glass and track and to provide a clean cosmetic edge. The plastic material may be polyvinyl and, in addition to providing improved cosmetic appearance, also minimizes water and air infiltration along the edges of the glass-to-track interface.
The present invention further addresses the reduction of stresses imparted to a boat windshield by providing an improvement of mounting the windshield to the deck of a boat. In the disclosed method, the windshield may be mounted at each end of the windshield frame and at one additional location that is just forward of the curve in the windshield as the windshield is curved around the forward portion of the boat deck. This arrangement provides essentially a three-point mounting system with a large section of the frame being allowed to float on the surface of the boat deck between the most rearward mounting point and a position forward of the curved portion of the windshield. Since most of the movement of the boat deck occurs in this region, this mounting arrangement reduces the stresses imparted to the windshield by movement of the boat deck.
The invention also addresses the issues of attachment of threaded members into a slot on a forward surface of a metal frame for a frangible sheet member. In the present form, threaded members such as buttons are attached to the metal frame by threading into a plastic insert having relatively thin sidewalls so that threading of the button causes the threads to cut through the plastic sidewalls and extend outward therefrom rather than expanding the sidewalls. In this manner, the threads of the insert cut into the actual metal material of the frame and bind directly to the frame rather than being attached by means of expansion of the plastic member. Accordingly, extended use of the attachment does not create wear such that the attachment becomes loose within the frame.